Manchester police on Tuesday released three of the men arrested in connection with the May 22 terrorist attack at pop concert in the British city.
A total of 11 people remain in British custody following the suicide bombing at Manchester Arena where US star Ariana Grande was performing.
Twenty-two people, including seven children, were killed in the attack.
Two men, aged 20 and 24, were released on Tuesday after being arrested in south Manchester on May 24 close to where bomber Salman Abedi lived.
A 37-year-old man, arrested a day later in the Blackley area of north Manchester, was also released without charge.
"The release of some people can be expected in investigations of this nature as we corroborate accounts that have been provided," said Russ Jackson, head of the north-west counter-terrorism unit.
Abedi's father and brother are also in detention in Libya, where authorities say the two brothers were both part of the Islamic State group which claimed responsibility for the deadly attack.
Born in Britain to Libyan parents, Abedi is believed to have returned from a trip to Libya a few days before the bombing.
Investigators said he bought most of the core components of the bomb himself and was often alone in the days leading up to the attack.
"It is vital that we make sure that he is not part of a wider network and we cannot rule this out yet. There remain a number of things that concern us about his behaviour prior to the attack and those of his associates which we need to get to the bottom of," said Jackson.
He stressed the need to find a blue suitcase used by Abedi, seen in CCTV images released by police.